Recently and continuing, personal computers (PC) are widely used not only by corporations but also by individuals at ordinary homes with improved performance and economy. There, optical disks, such as a CD (compact disk) and a DVD (digital versatile disk), attract attention as recording media providing great storage capacity for low prices, and optical disk apparatuses that use such optical disks as the object media of information recording are widely spread as peripheral devices of the PCs.
In this way, information (contents) such as music pieces, movies, pictures, and computer software can be easily copied to another optical disk, which gives great damage to providers of the contents.
Then, a “copy-once” practice has been introduced so that copying the content is allowed only once by using an ID. The practice is used by some contents provided by satellite broadcasting, cable TV, and the like so that no multiple copying operations are allowed. The practice will be widely used in the future. Hereafter, a set of contents, copying of which set is allowed only once, is called “a copy-once content”.
By the way, an optical disk can be degraded with a crack, dirt, and the like. In this case, if multiple copying of a set of contents in the degraded disk is allowed, copying may be performed. However, if the content is a “copy-once content”, it cannot be copied, and the content has to be purchased again. Further, in the case of a write-once optical disk (for example, a DVD+R disk, and a DVD−R disk), stored information (content) can be erased (Patent Reference 1).
Below, background relative to the write-once disk is further described.
Information recording apparatuses are widely used for storing contents (such as provided by satellite broadcasting and cable TV) in a recording medium that has a great storage capacity. The recording medium includes the optical disk, such as a DVD (digital versatile disk).
However, since the information (content) stored in the optical disk is digitized, the content can be duplicated without degrading quality of the content such as image and sound. Such copying is often an illegal operation that causes great damage to content providers.
Then, in order to prevent the illegal copying operation, some contents bear an ID so that only one copying operation is permitted. Such contents are called “copy-once contents”. Adding such IDs will be extensively used in the future.
By the way, the write-once optical disk that is widely used at present can be degraded by sunrays, a crack, dirt, etc. Generally, as a precaution, a backup copy is desired before the original disk becomes completely degraded, i.e., completely non-reproducible. However, an optical disk containing copy-once contents cannot be legally duplicated. In addition, various optical disks and apparatuses that are capable of preventing illegal copying operations and unauthorized use of contents have been devised (for example, Patent Reference 2 and Patent Reference 3).
However, such a devised optical disk disclosed by Patent Reference 2, and such devised data terminal apparatuses disclosed by Patent Reference 3 are expensive for general users.
[Patent reference 1] JPA H10-302265
[Patent reference 2] JPA 2000-163883
[Patent reference 3] JPA 2002-163577